The present invention relates to residential alarm systems for detecting dangerous conditions in multiple locations within a building. Specifically, a method and system for synchronizing audible warning appliances which are distributed throughout a home or other facility is described.
Alarm systems which detect dangerous conditions in a home, such as the presence of smoke, or carbon dioxide, are extensively used to prevent death or injury. In recent years, it has been the practice to interconnect different alarm units which are located in different rooms of a person""s home. Specifically, smoke detecting systems for warning inhabitants of a fire have been installed in individual rooms of a home and interconnected so that all alarms will sound if one alarm detects any combustion products produced by a fire. In this way, individuals located away from the source of combustion products are alerted to the danger of fire, as well as those in closer proximity to the fire. In accordance with various safety codes, these devices are equipped with a light-emitting source, so that the alarm which detects the smoke or other dangerous condition will provide a visual indication of the source of the dangerous conditions. In this way, it is possible for responding fire personnel to determine which of the units is sensing the alarm condition while the remaining devices distributed throughout the home provide an audible alarm.
The system interconnecting the various alarm units in a dwelling relies upon the sensing alarm to apply a voltage to a common conductor interconnecting each of the distributed alarm units. When the applied voltage is detected to be above a threshold value, typically three volts, the remaining alarms begin sounding their audible signaling horn. The common conductor carries a signaling voltage from the sensing alarm to each of the remaining alarms for triggering the audible responses from the remaining remote alarm devices.
The input/output connection to the common conductor is equipped with a filter to minimize the possibility of the random triggering of the alarm by voltages induced on the common conductor, as well as to minimize the effects of voltage spikes on the neutral of the power line which may inadvertently signal connected smoke detectors into an alarm condition.
The prior art interconnected smoke detector alarms included a test capability at each alarm. When an individual in a room having a smoke alarm activates the test feature, an audible signal is produced from the smoke alarm being tested. As long as the user releases the test switch within a brief period of time, the other units throughout the facility are not activated. However, the presence of the input filter of each smoke alarm connected to the common conductor resulted in a latent electrical charge being maintained on the filter capacitor which required several seconds to discharge. Following a test, or actual alarm condition which is transmitted on the common conductor, the input filters may remain charged to the point where each remote alarm unit can remain in a temporary alarm condition resulting in an objectionable false alarm.
The foregoing problem has been addressed in the prior art by applying a momentary low impedance from the common conductor to circuit ground following the generation of an alarm signal on the common conductor, quickly discharging the filter capacitors, avoiding the consequence of an inadvertent false alarm due to the stored charge.
The detected alarm condition in future alarm systems may represent one of several types of alarms. For instance, the danger of fire may be sensed with a smoke detector, and the danger from carbon monoxide poisoning may be sensed with a gas detector. Various authorities having jurisdiction have required manufacturers to generate different audible signaling patterns so that people hearing the respective alarms can distinguish between the different sensed dangers.
Using signaling formats of specific temporal patterns is made difficult if all detectors are not synchronized to produce the same audible pattern of warning signals. The unsynchronized alarms produce a cacophony of sounds which make discerning any particular pattern difficult.
The effectiveness of the connected alarm devices could, therefore, be enhanced by synchronizing the audible responses provided by each alarm device when responding to a remote unit which is detecting an alarm condition. The foregoing features which permit self tests to be made at each alarm, and which discharge each of the filter capacitors of the connected alarms following a test, provide the basis for a circuit which can be modified to permit synchronous signaling by each of the connected alarms.
The present invention provides an ability to synchronize the audible alarm sounds of interconnected alarm devices to more clearly distinguish the alarm as being either a smoke condition, or a carbon monoxide condition, or any other alarm condition which may be sensed at a given location, avoiding the cacophony of unsynchronized audible signals which obscure the nature of the detected condition.
An alarm device for responding to a locally generated alarm condition, which also responds to a remotely detected alarm condition, is provided by the invention. The alarm device includes a sensor which detects a local alarm condition such as smoke, carbon monoxide, explosive gas mixtures, etc., and sounds an audible, pulsed alarm when a dangerous condition is sensed. Each alarm device is equipped with a signal detector connected to a common conductor which detects an alarm voltage on the common conductor generated by a remote alarm device detecting an alarm condition. A transmitter circuit at the remote alarm device sends a pulsed signal to each connected alarm device, which is time synchronous with the audible alarm being generated by the remote alarm device, initiating a pulsed audible signal at each of the alarm devices. By generating a synchronized audible signal at each location, the homeowner, resident or the responding emergency personnel can quickly and correctly identify the specific alarm condition.